Fix "The Drupal\migrate\Plugin\migrate\process\Iterator is deprecated in Drupal 8.4.x and will be removed before Drupal 9.0.0. Instead, use Drupal\migrate\Plugin\migrate\process\SubProcess"

Nice work!

+++ b/core/modules/migrate/tests/src/Unit/process/IteratorTest.php
@@ -18,7 +18,7 @@ class IteratorTest extends MigrateTestCase {
-   * @var \Drupal\migrate\Plugin\migrate\process\TestIterator
+   * @var \Drupal\migrate\Plugin\migrate\process\SubProcess

This is actually a Drupal\migrate\Plugin\migrate\process\Iterator - it is currently incorrect and the patch change is still not right. This is a legacy test - we should be adding an @expectedDeprecation annotation to the test and fixing this to point to the deprecated class.

The other changes look good.

Cleaning up tags.

Looks great now :)

+++ b/core/modules/migrate/tests/src/Unit/process/IteratorTest.php
@@ -21,6 +19,7 @@ class IteratorTest extends MigrateTestCase {
+   * @expectedDeprecation The Drupal\migrate\Plugin\migrate\process\Iterator is deprecated in Drupal 8.4.x and will be removed before Drupal 9.0.0. Instead, use Drupal\migrate\Plugin\migrate\process\SubProcess

The @expectedDeprecation annotation needs to be placed in the documentation block of a test method. In this case, it needs to be in the testIterator() method of this test class.

You can find an example of how this works in the \Drupal\Tests\link\Unit\Plugin\migrate\cckfield\LinkCckTest test class, and the testProcessCckFieldValues() test method.

Looks great now :)

Committed and pushed 282eb36c14 to 8.6.x and 5781652137 to 8.5.x. Thanks!

Backported to 8.5.x since all the changes are either docs or tests.